/*
 * Copyright (c) 1982, 1986, 1988, 1990, 1993, 1994
 *	The Regents of the University of California.  All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 * 3. Neither the name of the University nor the names of its contributors
 *    may be used to endorse or promote products derived from this software
 *    without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 *
 *	@(#)tcp_input.c	8.5 (Berkeley) 4/10/94
 * tcp_input.c,v 1.10 1994/10/13 18:36:32 wollman Exp
 */

/*
 * Changes and additions relating to SLiRP
 * Copyright (c) 1995 Danny Gasparovski.
 *
 * Please read the file COPYRIGHT for the
 * terms and conditions of the copyright.
 */

#include <stdlib.h>
#include "slirp/slirp.h"
#include "slirp/ip_icmp.h"

struct SLIRPsocket tcb;

int tcprexmtthresh = 3;
struct SLIRPsocket *tcp_last_so = &tcb;

tcp_seq tcp_iss; /* tcp initial send seq # */

#define TCP_PAWS_IDLE (24 * 24 * 60 * 60 * PR_SLOWHZ)

/* for modulo comparisons of timestamps */
#define TSTMP_LT(a, b) ((int)((a) - (b)) < 0)
#define TSTMP_GEQ(a, b) ((int)((a) - (b)) >= 0)

/*
 * Insert segment ti into reassembly queue of tcp with
 * control block tp.  Return TH_FIN if reassembly now includes
 * a segment with FIN.  The macro form does the common case inline
 * (segment is the next to be received on an established connection,
 * and the queue is empty), avoiding linkage into and removal
 * from the queue and repetition of various conversions.
 * Set DELACK for segments received in order, but ack immediately
 * when segments are out of order (so fast retransmit can work).
 */
#ifdef TCP_ACK_HACK
#define TCP_REASS(tp, ti, m, so, flags)                                                                                          \
        {                                                                                                                        \
                if ((ti)->ti_seq == (tp)->rcv_nxt && tcpfrag_list_empty(tp) && (tp)->t_state == TCPS_ESTABLISHED) {              \
                        if (ti->ti_flags & TH_PUSH)                                                                              \
                                tp->t_flags |= TF_ACKNOW;                                                                        \
                        else                                                                                                     \
                                tp->t_flags |= TF_DELACK;                                                                        \
                        (tp)->rcv_nxt += (ti)->ti_len;                                                                           \
                        flags = (ti)->ti_flags & TH_FIN;                                                                         \
                        tcpstat.tcps_rcvpack++;                                                                                  \
                        tcpstat.tcps_rcvbyte += (ti)->ti_len;                                                                    \
                        if (so->so_emu) {                                                                                        \
                                if (tcp_emu((so), (m)))                                                                          \
                                        sbappend((so), (m));                                                                     \
                        } else                                                                                                   \
                                sbappend((so), (m));                                                                             \
                        /*               sorwakeup(so); */                                                                       \
                } else {                                                                                                         \
                        (flags) = tcp_reass((tp), (ti), (m));                                                                    \
                        tp->t_flags |= TF_ACKNOW;                                                                                \
                }                                                                                                                \
        }
#else
#define TCP_REASS(tp, ti, m, so, flags)                                                                                          \
        {                                                                                                                        \
                if ((ti)->ti_seq == (tp)->rcv_nxt && tcpfrag_list_empty(tp) && (tp)->t_state == TCPS_ESTABLISHED) {              \
                        tp->t_flags |= TF_DELACK;                                                                                \
                        (tp)->rcv_nxt += (ti)->ti_len;                                                                           \
                        flags = (ti)->ti_flags & TH_FIN;                                                                         \
                        tcpstat.tcps_rcvpack++;                                                                                  \
                        tcpstat.tcps_rcvbyte += (ti)->ti_len;                                                                    \
                        if (so->so_emu) {                                                                                        \
                                if (tcp_emu((so), (m)))                                                                          \
                                        sbappend(so, (m));                                                                       \
                        } else                                                                                                   \
                                sbappend((so), (m));                                                                             \
                        /*		sorwakeup(so); */                                                                                    \
                } else {                                                                                                         \
                        (flags) = tcp_reass((tp), (ti), (m));                                                                    \
                        tp->t_flags |= TF_ACKNOW;                                                                                \
                }                                                                                                                \
        }
#endif

int tcp_reass(tp, ti, m) struct tcpcb *tp;
struct tcpiphdr *ti;
struct SLIRPmbuf *m;
{
        struct tcpiphdr *q;
        struct SLIRPsocket *so = tp->t_socket;
        int flags;

        /*
         * Call with ti==0 after become established to
         * force pre-ESTABLISHED data up to user socket.
         */
        if (ti == 0)
                goto present;

        /*
         * Find a segment which begins after this one does.
         */
        for (q = tcpfrag_list_first(tp); !tcpfrag_list_end(q, tp); q = tcpiphdr_next(q))
                if (SEQ_GT(q->ti_seq, ti->ti_seq))
                        break;

        /*
         * If there is a preceding segment, it may provide some of
         * our data already.  If so, drop the data from the incoming
         * segment.  If it provides all of our data, drop us.
         */
        if (!tcpfrag_list_end(tcpiphdr_prev(q), tp)) {
                int i;
                q = tcpiphdr_prev(q);
                /* conversion to int (in i) handles seq wraparound */
                i = q->ti_seq + q->ti_len - ti->ti_seq;
                if (i > 0) {
                        if (i >= ti->ti_len) {
                                tcpstat.tcps_rcvduppack++;
                                tcpstat.tcps_rcvdupbyte += ti->ti_len;
                                m_freem(m);
                                /*
                                 * Try to present any queued data
                                 * at the left window edge to the user.
                                 * This is needed after the 3-WHS
                                 * completes.
                                 */
                                goto present; /* ??? */
                        }
                        m_adj(m, i);
                        ti->ti_len -= i;
                        ti->ti_seq += i;
                }
                q = tcpiphdr_next(q);
        }
        tcpstat.tcps_rcvoopack++;
        tcpstat.tcps_rcvoobyte += ti->ti_len;
        ti->ti_mbuf = (struct mbuf *)m;

        /*
         * While we overlap succeeding segments trim them or,
         * if they are completely covered, dequeue them.
         */
        while (!tcpfrag_list_end(q, tp)) {
                int i = (ti->ti_seq + ti->ti_len) - q->ti_seq;
                if (i <= 0)
                        break;
                if (i < q->ti_len) {
                        q->ti_seq += i;
                        q->ti_len -= i;
                        m_adj((struct SLIRPmbuf *)q->ti_mbuf, i);
                        break;
                }
                q = tcpiphdr_next(q);
                m = (struct SLIRPmbuf *)tcpiphdr_prev(q)->ti_mbuf;
                remque(tcpiphdr2qlink(tcpiphdr_prev(q)));
                m_freem(m);
        }

        /*
         * Stick new segment in its place.
         */
        insque(tcpiphdr2qlink(ti), tcpiphdr2qlink(tcpiphdr_prev(q)));

present:
        /*
         * Present data to user, advancing rcv_nxt through
         * completed sequence space.
         */
        if (!TCPS_HAVEESTABLISHED(tp->t_state))
                return (0);
        ti = tcpfrag_list_first(tp);
        if (tcpfrag_list_end(ti, tp) || ti->ti_seq != tp->rcv_nxt)
                return (0);
        if (tp->t_state == TCPS_SYN_RECEIVED && ti->ti_len)
                return (0);
        do {
                tp->rcv_nxt += ti->ti_len;
                flags = ti->ti_flags & TH_FIN;
                remque(tcpiphdr2qlink(ti));
                m = (struct SLIRPmbuf *)ti->ti_mbuf;
                ti = tcpiphdr_next(ti);
                /*		if (so->so_state & SS_FCANTRCVMORE) */
                if (so->so_state & SS_FCANTSENDMORE)
                        m_freem(m);
                else {
                        if (so->so_emu) {
                                if (tcp_emu(so, m))
                                        sbappend(so, m);
                        } else
                                sbappend(so, m);
                }
        } while (ti != (struct tcpiphdr *)tp && ti->ti_seq == tp->rcv_nxt);
        /*	sorwakeup(so); */
        return (flags);
}

/*
 * TCP input routine, follows pages 65-76 of the
 * protocol specification dated September, 1981 very closely.
 */
void tcp_input(m, iphlen, inso) struct SLIRPmbuf *m;
int iphlen;
struct SLIRPsocket *inso;
{
        struct ip save_ip, *ip;
        struct tcpiphdr *ti;
        SLIRPcaddr_t optp = NULL;
        int optlen = 0;
        int len, tlen, off;
        struct tcpcb *tp = 0;
        int tiflags;
        struct SLIRPsocket *so = 0;
        int todrop, acked, ourfinisacked, needoutput = 0;
        /*	int dropsocket = 0; */
        int iss = 0;
        u_long tiwin;
        int ret;
        /*	int ts_present = 0; */

        DEBUG_CALL("tcp_input");
        DEBUG_ARGS((dfd, " m = %8lx  iphlen = %2d  inso = %lx\n", (long)m, iphlen, (long)inso));

        /*
         * If called with m == 0, then we're continuing the connect
         */
        if (m == NULL) {
                so = inso;

                /* Re-set a few variables */
                tp = sototcpcb(so);
                m = so->so_m;
                so->so_m = 0;
                ti = so->so_ti;
                tiwin = ti->ti_win;
                tiflags = ti->ti_flags;

                goto cont_conn;
        }

        tcpstat.tcps_rcvtotal++;
        /*
         * Get IP and TCP header together in first SLIRPmbuf.
         * Note: IP leaves IP header in first SLIRPmbuf.
         */
        ti = mtod(m, struct tcpiphdr *);
        if (iphlen > sizeof(struct ip)) {
                ip_stripoptions(m, (struct SLIRPmbuf *)0);
                iphlen = sizeof(struct ip);
        }
        /* XXX Check if too short */

        /*
         * Save a copy of the IP header in case we want restore it
         * for sending an ICMP error message in response.
         */
        ip = mtod(m, struct ip *);
        save_ip = *ip;
        save_ip.ip_len += iphlen;

        /*
         * Checksum extended TCP header and data.
         */
        tlen = ((struct ip *)ti)->ip_len;
        tcpiphdr2qlink(ti)->next = tcpiphdr2qlink(ti)->prev = 0;
        memset(&ti->ti_i.ih_mbuf, 0, sizeof(struct mbuf_ptr));
        ti->ti_x1 = 0;
        ti->ti_len = htons((u_int16_t)tlen);
        len = sizeof(struct ip) + tlen;
        /* keep checksum for ICMP reply
         * ti->ti_sum = cksum(m, len);
         * if (ti->ti_sum) { */
        if (cksum(m, len)) {
                tcpstat.tcps_rcvbadsum++;
                goto drop;
        }

        /*
         * Check that TCP offset makes sense,
         * pull out TCP options and adjust length.		XXX
         */
        off = ti->ti_off << 2;
        if (off < sizeof(struct tcphdr) || off > tlen) {
                tcpstat.tcps_rcvbadoff++;
                goto drop;
        }
        tlen -= off;
        ti->ti_len = tlen;
        if (off > sizeof(struct tcphdr)) {
                optlen = off - sizeof(struct tcphdr);
                optp = mtod(m, SLIRPcaddr_t) + sizeof(struct tcpiphdr);

                /*
                 * Do quick retrieval of timestamp options ("options
                 * prediction?").  If timestamp is the only option and it's
                 * formatted as recommended in RFC 1323 appendix A, we
                 * quickly get the values now and not bother calling
                 * tcp_dooptions(), etc.
                 */
                /*		if ((optlen == TCPOLEN_TSTAMP_APPA ||
                 *		     (optlen > TCPOLEN_TSTAMP_APPA &&
                 *			optp[TCPOLEN_TSTAMP_APPA] == TCPOPT_EOL)) &&
                 *		     *(u_int32_t *)optp == htonl(TCPOPT_TSTAMP_HDR) &&
                 *		     (ti->ti_flags & TH_SYN) == 0) {
                 *			ts_present = 1;
                 *			ts_val = ntohl(*(u_int32_t *)(optp + 4));
                 *			ts_ecr = ntohl(*(u_int32_t *)(optp + 8));
                 *			optp = NULL;   / * we've parsed the options * /
                 *		}
                 */
        }
        tiflags = ti->ti_flags;

        /*
         * Convert TCP protocol specific fields to host format.
         */
        NTOHL(ti->ti_seq);
        NTOHL(ti->ti_ack);
        NTOHS(ti->ti_win);
        NTOHS(ti->ti_urp);

        /*
         * Drop TCP, IP headers and TCP options.
         */
        m->m_data += sizeof(struct tcpiphdr) + off - sizeof(struct tcphdr);
        m->m_len -= sizeof(struct tcpiphdr) + off - sizeof(struct tcphdr);

        /*
         * Locate pcb for segment.
         */
findso:
        so = tcp_last_so;
        if (so->so_fport != ti->ti_dport || so->so_lport != ti->ti_sport || so->so_laddr.s_addr != ti->ti_src.s_addr ||
            so->so_faddr.s_addr != ti->ti_dst.s_addr) {
                so = solookup(&tcb, ti->ti_src, ti->ti_sport, ti->ti_dst, ti->ti_dport);
                if (so)
                        tcp_last_so = so;
                ++tcpstat.tcps_socachemiss;
        }

        /*
         * If the state is CLOSED (i.e., TCB does not exist) then
         * all data in the incoming segment is discarded.
         * If the TCB exists but is in CLOSED state, it is embryonic,
         * but should either do a listen or a connect soon.
         *
         * state == CLOSED means we've done socreate() but haven't
         * attached it to a protocol yet...
         *
         * XXX If a TCB does not exist, and the TH_SYN flag is
         * the only flag set, then create a session, mark it
         * as if it was LISTENING, and continue...
         */
        if (so == 0) {
                if ((tiflags & (TH_SYN | TH_FIN | TH_RST | TH_URG | TH_ACK)) != TH_SYN)
                        goto dropwithreset;

                if ((so = socreate()) == NULL)
                        goto dropwithreset;
                if (tcp_attach(so) < 0) {
                        free(so); /* Not sofree (if it failed, it's not insqued) */
                        goto dropwithreset;
                }

                sbreserve(&so->so_snd, tcp_sndspace);
                sbreserve(&so->so_rcv, tcp_rcvspace);

                /*		tcp_last_so = so; */ /* XXX ? */
                /*		tp = sototcpcb(so);    */

                so->so_laddr = ti->ti_src;
                so->so_lport = ti->ti_sport;
                so->so_faddr = ti->ti_dst;
                so->so_fport = ti->ti_dport;

                if ((so->so_iptos = tcp_tos(so)) == 0)
                        so->so_iptos = ((struct ip *)ti)->ip_tos;

                tp = sototcpcb(so);
                tp->t_state = TCPS_LISTEN;
        }

        /*
         * If this is a still-connecting socket, this probably
         * a retransmit of the SYN.  Whether it's a retransmit SYN
         * or something else, we nuke it.
         */
        if (so->so_state & SS_ISFCONNECTING)
                goto drop;

        tp = sototcpcb(so);

        /* XXX Should never fail */
        if (tp == 0)
                goto dropwithreset;
        if (tp->t_state == TCPS_CLOSED)
                goto drop;

        /* Unscale the window into a 32-bit value. */
        /*	if ((tiflags & TH_SYN) == 0)
         *		tiwin = ti->ti_win << tp->snd_scale;
         *	else
         */
        tiwin = ti->ti_win;

        /*
         * Segment received on connection.
         * Reset idle time and keep-alive timer.
         */
        tp->t_idle = 0;
        if (so_options)
                tp->t_timer[TCPT_KEEP] = tcp_keepintvl;
        else
                tp->t_timer[TCPT_KEEP] = tcp_keepidle;

        /*
         * Process options if not in LISTEN state,
         * else do it below (after getting remote address).
         */
        if (optp && tp->t_state != TCPS_LISTEN)
                tcp_dooptions(tp, (u_char *)optp, optlen, ti);
        /* , */
        /*			&ts_present, &ts_val, &ts_ecr); */

        /*
         * Header prediction: check for the two common cases
         * of a uni-directional data xfer.  If the packet has
         * no control flags, is in-sequence, the window didn't
         * change and we're not retransmitting, it's a
         * candidate.  If the length is zero and the ack moved
         * forward, we're the sender side of the xfer.  Just
         * free the data acked & wake any higher level process
         * that was blocked waiting for space.  If the length
         * is non-zero and the ack didn't move, we're the
         * receiver side.  If we're getting packets in-order
         * (the reassembly queue is empty), add the data to
         * the socket buffer and note that we need a delayed ack.
         *
         * XXX Some of these tests are not needed
         * eg: the tiwin == tp->snd_wnd prevents many more
         * predictions.. with no *real* advantage..
         */
        if (tp->t_state == TCPS_ESTABLISHED && (tiflags & (TH_SYN | TH_FIN | TH_RST | TH_URG | TH_ACK)) == TH_ACK &&
            /*	    (!ts_present || TSTMP_GEQ(ts_val, tp->ts_recent)) && */
            ti->ti_seq == tp->rcv_nxt && tiwin && tiwin == tp->snd_wnd && tp->snd_nxt == tp->snd_max) {
                /*
                 * If last ACK falls within this segment's sequence numbers,
                 *  record the timestamp.
                 */
                /*		if (ts_present && SEQ_LEQ(ti->ti_seq, tp->last_ack_sent) &&
                 *		   SEQ_LT(tp->last_ack_sent, ti->ti_seq + ti->ti_len)) {
                 *			tp->ts_recent_age = tcp_now;
                 *			tp->ts_recent = ts_val;
                 *		}
                 */
                if (ti->ti_len == 0) {
                        if (SEQ_GT(ti->ti_ack, tp->snd_una) && SEQ_LEQ(ti->ti_ack, tp->snd_max) && tp->snd_cwnd >= tp->snd_wnd) {
                                /*
                                 * this is a pure ack for outstanding data.
                                 */
                                ++tcpstat.tcps_predack;
                                /*				if (ts_present)
                                 *					tcp_xmit_timer(tp, tcp_now-ts_ecr+1);
                                 *				else
                                 */
                                if (tp->t_rtt && SEQ_GT(ti->ti_ack, tp->t_rtseq))
                                        tcp_xmit_timer(tp, tp->t_rtt);
                                acked = ti->ti_ack - tp->snd_una;
                                tcpstat.tcps_rcvackpack++;
                                tcpstat.tcps_rcvackbyte += acked;
                                sbdrop(&so->so_snd, acked);
                                tp->snd_una = ti->ti_ack;
                                m_freem(m);

                                /*
                                 * If all outstanding data are acked, stop
                                 * retransmit timer, otherwise restart timer
                                 * using current (possibly backed-off) value.
                                 * If process is waiting for space,
                                 * wakeup/selwakeup/signal.  If data
                                 * are ready to send, let tcp_output
                                 * decide between more output or persist.
                                 */
                                if (tp->snd_una == tp->snd_max)
                                        tp->t_timer[TCPT_REXMT] = 0;
                                else if (tp->t_timer[TCPT_PERSIST] == 0)
                                        tp->t_timer[TCPT_REXMT] = tp->t_rxtcur;

                                /*
                                 * There's room in so_snd, sowwakup will read()
                                 * from the socket if we can
                                 */
                                /*				if (so->so_snd.sb_flags & SB_NOTIFY)
                                 *					sowwakeup(so);
                                 */
                                /*
                                 * This is called because sowwakeup might have
                                 * put data into so_snd.  Since we don't so sowwakeup,
                                 * we don't need this.. XXX???
                                 */
                                if (so->so_snd.sb_cc)
                                        (void)tcp_output(tp);

                                return;
                        }
                } else if (ti->ti_ack == tp->snd_una && tcpfrag_list_empty(tp) && ti->ti_len <= sbspace(&so->so_rcv)) {
                        /*
                         * this is a pure, in-sequence data packet
                         * with nothing on the reassembly queue and
                         * we have enough buffer space to take it.
                         */
                        ++tcpstat.tcps_preddat;
                        tp->rcv_nxt += ti->ti_len;
                        tcpstat.tcps_rcvpack++;
                        tcpstat.tcps_rcvbyte += ti->ti_len;
                        /*
                         * Add data to socket buffer.
                         */
                        if (so->so_emu) {
                                if (tcp_emu(so, m))
                                        sbappend(so, m);
                        } else
                                sbappend(so, m);

                        /*
                         * XXX This is called when data arrives.  Later, check
                         * if we can actually write() to the socket
                         * XXX Need to check? It's be NON_BLOCKING
                         */
                        /*			sorwakeup(so); */

                        /*
                         * If this is a short packet, then ACK now - with Nagel
                         *	congestion avoidance sender won't send more until
                         *	he gets an ACK.
                         *
                         * It is better to not delay acks at all to maximize
                         * TCP throughput.  See RFC 2581.
                         */
                        tp->t_flags |= TF_ACKNOW;
                        tcp_output(tp);
                        return;
                }
        } /* header prediction */
        /*
         * Calculate amount of space in receive window,
         * and then do TCP input processing.
         * Receive window is amount of space in rcv queue,
         * but not less than advertised window.
         */
        {
                int win;
                win = sbspace(&so->so_rcv);
                if (win < 0)
                        win = 0;
                tp->rcv_wnd = max(win, (int)(tp->rcv_adv - tp->rcv_nxt));
        }

        switch (tp->t_state) {

                /*
                 * If the state is LISTEN then ignore segment if it contains an RST.
                 * If the segment contains an ACK then it is bad and send a RST.
                 * If it does not contain a SYN then it is not interesting; drop it.
                 * Don't bother responding if the destination was a broadcast.
                 * Otherwise initialize tp->rcv_nxt, and tp->irs, select an initial
                 * tp->iss, and send a segment:
                 *     <SEQ=ISS><ACK=RCV_NXT><CTL=SYN,ACK>
                 * Also initialize tp->snd_nxt to tp->iss+1 and tp->snd_una to tp->iss.
                 * Fill in remote peer address fields if not previously specified.
                 * Enter SYN_RECEIVED state, and process any other fields of this
                 * segment in this state.
                 */
        case TCPS_LISTEN: {

                if (tiflags & TH_RST)
                        goto drop;
                if (tiflags & TH_ACK)
                        goto dropwithreset;
                if ((tiflags & TH_SYN) == 0)
                        goto drop;

                /*
                 * This has way too many gotos...
                 * But a bit of spaghetti code never hurt anybody :)
                 */

                /*
                 * If this is destined for the control address, then flag to
                 * tcp_ctl once connected, otherwise connect
                 */
                if ((so->so_faddr.s_addr & htonl(0xffffff00)) == special_addr.s_addr) {
                        int lastbyte = ntohl(so->so_faddr.s_addr) & 0xff;
                        if (lastbyte != CTL_ALIAS && lastbyte != CTL_DNS) {
#if 0
				if(lastbyte==CTL_CMD || lastbyte==CTL_EXEC) {
				  /* Command or exec adress */
				  so->so_state |= SS_CTL;
				} else
#endif
                                {
                                        /* May be an add exec */
                                        struct ex_list *ex_ptr;
                                        for (ex_ptr = exec_list; ex_ptr; ex_ptr = ex_ptr->ex_next) {
                                                if (ex_ptr->ex_fport == so->so_fport && lastbyte == ex_ptr->ex_addr) {
                                                        so->so_state |= SS_CTL;
                                                        break;
                                                }
                                        }
                                }
                                if (so->so_state & SS_CTL)
                                        goto cont_input;
                        }
                        /* CTL_ALIAS: Do nothing, tcp_fconnect will be called on it */
                }

                if (so->so_emu & EMU_NOCONNECT) {
                        so->so_emu &= ~EMU_NOCONNECT;
                        goto cont_input;
                }

                if ((tcp_fconnect(so) == -1) && (errno != EINPROGRESS) && (errno != EWOULDBLOCK)) {
                        u_char code = ICMP_UNREACH_NET;
                        DEBUG_MISC((dfd, " tcp fconnect errno = %d-%s\n", errno, strerror(errno)));
                        if (errno == ECONNREFUSED) {
                                /* ACK the SYN, send RST to refuse the connection */
                                tcp_respond(tp, ti, m, ti->ti_seq + 1, (tcp_seq)0, TH_RST | TH_ACK);
                        } else {
                                if (errno == EHOSTUNREACH)
                                        code = ICMP_UNREACH_HOST;
                                HTONL(ti->ti_seq); /* restore tcp header */
                                HTONL(ti->ti_ack);
                                HTONS(ti->ti_win);
                                HTONS(ti->ti_urp);
                                m->m_data -= sizeof(struct tcpiphdr) + off - sizeof(struct tcphdr);
                                m->m_len += sizeof(struct tcpiphdr) + off - sizeof(struct tcphdr);
                                *ip = save_ip;
                                icmp_error(m, ICMP_UNREACH, code, 0, strerror(errno));
                        }
                        tp = tcp_close(tp);
                        m_free(m);
                } else {
                        /*
                         * Haven't connected yet, save the current SLIRPmbuf
                         * and ti, and return
                         * XXX Some OS's don't tell us whether the connect()
                         * succeeded or not.  So we must time it out.
                         */
                        so->so_m = m;
                        so->so_ti = ti;
                        tp->t_timer[TCPT_KEEP] = TCPTV_KEEP_INIT;
                        tp->t_state = TCPS_SYN_RECEIVED;
                }
                return;

        cont_conn:
                /* m==NULL
                 * Check if the connect succeeded
                 */
                if (so->so_state & SS_NOFDREF) {
                        tp = tcp_close(tp);
                        goto dropwithreset;
                }
        cont_input:
                tcp_template(tp);

                if (optp)
                        tcp_dooptions(tp, (u_char *)optp, optlen, ti);
                /* , */
                /*				&ts_present, &ts_val, &ts_ecr); */

                if (iss)
                        tp->iss = iss;
                else
                        tp->iss = tcp_iss;
                tcp_iss += TCP_ISSINCR / 2;
                tp->irs = ti->ti_seq;
                tcp_sendseqinit(tp);
                tcp_rcvseqinit(tp);
                tp->t_flags |= TF_ACKNOW;
                tp->t_state = TCPS_SYN_RECEIVED;
                tp->t_timer[TCPT_KEEP] = TCPTV_KEEP_INIT;
                tcpstat.tcps_accepts++;
                goto trimthenstep6;
        } /* case TCPS_LISTEN */

                /*
                 * If the state is SYN_SENT:
                 *	if seg contains an ACK, but not for our SYN, drop the input.
                 *	if seg contains a RST, then drop the connection.
                 *	if seg does not contain SYN, then drop it.
                 * Otherwise this is an acceptable SYN segment
                 *	initialize tp->rcv_nxt and tp->irs
                 *	if seg contains ack then advance tp->snd_una
                 *	if SYN has been acked change to ESTABLISHED else SYN_RCVD state
                 *	arrange for segment to be acked (eventually)
                 *	continue processing rest of data/controls, beginning with URG
                 */
        case TCPS_SYN_SENT:
                if ((tiflags & TH_ACK) && (SEQ_LEQ(ti->ti_ack, tp->iss) || SEQ_GT(ti->ti_ack, tp->snd_max)))
                        goto dropwithreset;

                if (tiflags & TH_RST) {
                        if (tiflags & TH_ACK)
                                tp = tcp_drop(tp, 0); /* XXX Check t_softerror! */
                        goto drop;
                }

                if ((tiflags & TH_SYN) == 0)
                        goto drop;
                if (tiflags & TH_ACK) {
                        tp->snd_una = ti->ti_ack;
                        if (SEQ_LT(tp->snd_nxt, tp->snd_una))
                                tp->snd_nxt = tp->snd_una;
                }

                tp->t_timer[TCPT_REXMT] = 0;
                tp->irs = ti->ti_seq;
                tcp_rcvseqinit(tp);
                tp->t_flags |= TF_ACKNOW;
                if (tiflags & TH_ACK && SEQ_GT(tp->snd_una, tp->iss)) {
                        tcpstat.tcps_connects++;
                        soisfconnected(so);
                        tp->t_state = TCPS_ESTABLISHED;

                        /* Do window scaling on this connection? */
                        /*			if ((tp->t_flags & (TF_RCVD_SCALE|TF_REQ_SCALE)) ==
                         *				(TF_RCVD_SCALE|TF_REQ_SCALE)) {
                         * 				tp->snd_scale = tp->requested_s_scale;
                         *				tp->rcv_scale = tp->request_r_scale;
                         *			}
                         */
                        (void)tcp_reass(tp, (struct tcpiphdr *)0, (struct SLIRPmbuf *)0);
                        /*
                         * if we didn't have to retransmit the SYN,
                         * use its rtt as our initial srtt & rtt var.
                         */
                        if (tp->t_rtt)
                                tcp_xmit_timer(tp, tp->t_rtt);
                } else
                        tp->t_state = TCPS_SYN_RECEIVED;

        trimthenstep6:
                /*
                 * Advance ti->ti_seq to correspond to first data byte.
                 * If data, trim to stay within window,
                 * dropping FIN if necessary.
                 */
                ti->ti_seq++;
                if (ti->ti_len > tp->rcv_wnd) {
                        todrop = ti->ti_len - tp->rcv_wnd;
                        m_adj(m, -todrop);
                        ti->ti_len = tp->rcv_wnd;
                        tiflags &= ~TH_FIN;
                        tcpstat.tcps_rcvpackafterwin++;
                        tcpstat.tcps_rcvbyteafterwin += todrop;
                }
                tp->snd_wl1 = ti->ti_seq - 1;
                tp->rcv_up = ti->ti_seq;
                goto step6;
        } /* switch tp->t_state */
        /*
         * States other than LISTEN or SYN_SENT.
         * First check timestamp, if present.
         * Then check that at least some bytes of segment are within
         * receive window.  If segment begins before rcv_nxt,
         * drop leading data (and SYN); if nothing left, just ack.
         *
         * RFC 1323 PAWS: If we have a timestamp reply on this segment
         * and it's less than ts_recent, drop it.
         */
        /*	if (ts_present && (tiflags & TH_RST) == 0 && tp->ts_recent &&
         *	    TSTMP_LT(ts_val, tp->ts_recent)) {
         *
         */                /* Check to see if ts_recent is over 24 days old.  */
        /*		if ((int)(tcp_now - tp->ts_recent_age) > TCP_PAWS_IDLE) {
         */                        /*
 *			 * Invalidate ts_recent.  If this segment updates
 *			 * ts_recent, the age will be reset later and ts_recent
 *			 * will get a valid value.  If it does not, setting
 *			 * ts_recent to zero will at least satisfy the
 *			 * requirement that zero be placed in the timestamp
 *			 * echo reply when ts_recent isn't valid.  The
 *			 * age isn't reset until we get a valid ts_recent
 *			 * because we don't want out-of-order segments to be
 *			 * dropped when ts_recent is old.
 *			 */
        /*			tp->ts_recent = 0;
         *		} else {
         *			tcpstat.tcps_rcvduppack++;
         *			tcpstat.tcps_rcvdupbyte += ti->ti_len;
         *			tcpstat.tcps_pawsdrop++;
         *			goto dropafterack;
         *		}
         *	}
         */

        todrop = tp->rcv_nxt - ti->ti_seq;
        if (todrop > 0) {
                if (tiflags & TH_SYN) {
                        tiflags &= ~TH_SYN;
                        ti->ti_seq++;
                        if (ti->ti_urp > 1)
                                ti->ti_urp--;
                        else
                                tiflags &= ~TH_URG;
                        todrop--;
                }
                /*
                 * Following if statement from Stevens, vol. 2, p. 960.
                 */
                if (todrop > ti->ti_len || (todrop == ti->ti_len && (tiflags & TH_FIN) == 0)) {
                        /*
                         * Any valid FIN must be to the left of the window.
                         * At this point the FIN must be a duplicate or out
                         * of sequence; drop it.
                         */
                        tiflags &= ~TH_FIN;

                        /*
                         * Send an ACK to resynchronize and drop any data.
                         * But keep on processing for RST or ACK.
                         */
                        tp->t_flags |= TF_ACKNOW;
                        todrop = ti->ti_len;
                        tcpstat.tcps_rcvduppack++;
                        tcpstat.tcps_rcvdupbyte += todrop;
                } else {
                        tcpstat.tcps_rcvpartduppack++;
                        tcpstat.tcps_rcvpartdupbyte += todrop;
                }
                m_adj(m, todrop);
                ti->ti_seq += todrop;
                ti->ti_len -= todrop;
                if (ti->ti_urp > todrop)
                        ti->ti_urp -= todrop;
                else {
                        tiflags &= ~TH_URG;
                        ti->ti_urp = 0;
                }
        }
        /*
         * If new data are received on a connection after the
         * user processes are gone, then RST the other end.
         */
        if ((so->so_state & SS_NOFDREF) && tp->t_state > TCPS_CLOSE_WAIT && ti->ti_len) {
                tp = tcp_close(tp);
                tcpstat.tcps_rcvafterclose++;
                goto dropwithreset;
        }

        /*
         * If segment ends after window, drop trailing data
         * (and PUSH and FIN); if nothing left, just ACK.
         */
        todrop = (ti->ti_seq + ti->ti_len) - (tp->rcv_nxt + tp->rcv_wnd);
        if (todrop > 0) {
                tcpstat.tcps_rcvpackafterwin++;
                if (todrop >= ti->ti_len) {
                        tcpstat.tcps_rcvbyteafterwin += ti->ti_len;
                        /*
                         * If a new connection request is received
                         * while in TIME_WAIT, drop the old connection
                         * and start over if the sequence numbers
                         * are above the previous ones.
                         */
                        if (tiflags & TH_SYN && tp->t_state == TCPS_TIME_WAIT && SEQ_GT(ti->ti_seq, tp->rcv_nxt)) {
                                iss = tp->rcv_nxt + TCP_ISSINCR;
                                tp = tcp_close(tp);
                                goto findso;
                        }
                        /*
                         * If window is closed can only take segments at
                         * window edge, and have to drop data and PUSH from
                         * incoming segments.  Continue processing, but
                         * remember to ack.  Otherwise, drop segment
                         * and ack.
                         */
                        if (tp->rcv_wnd == 0 && ti->ti_seq == tp->rcv_nxt) {
                                tp->t_flags |= TF_ACKNOW;
                                tcpstat.tcps_rcvwinprobe++;
                        } else
                                goto dropafterack;
                } else
                        tcpstat.tcps_rcvbyteafterwin += todrop;
                m_adj(m, -todrop);
                ti->ti_len -= todrop;
                tiflags &= ~(TH_PUSH | TH_FIN);
        }

        /*
         * If last ACK falls within this segment's sequence numbers,
         * record its timestamp.
         */
        /*	if (ts_present && SEQ_LEQ(ti->ti_seq, tp->last_ack_sent) &&
         *	    SEQ_LT(tp->last_ack_sent, ti->ti_seq + ti->ti_len +
         *		   ((tiflags & (TH_SYN|TH_FIN)) != 0))) {
         *		tp->ts_recent_age = tcp_now;
         *		tp->ts_recent = ts_val;
         *	}
         */

        /*
         * If the RST bit is set examine the state:
         *    SYN_RECEIVED STATE:
         *	If passive open, return to LISTEN state.
         *	If active open, inform user that connection was refused.
         *    ESTABLISHED, FIN_WAIT_1, FIN_WAIT2, CLOSE_WAIT STATES:
         *	Inform user that connection was reset, and close tcb.
         *    CLOSING, LAST_ACK, TIME_WAIT STATES
         *	Close the tcb.
         */
        if (tiflags & TH_RST)
                switch (tp->t_state) {

                case TCPS_SYN_RECEIVED:
                        /*		so->so_error = ECONNREFUSED; */
                        goto close;

                case TCPS_ESTABLISHED:
                case TCPS_FIN_WAIT_1:
                case TCPS_FIN_WAIT_2:
                case TCPS_CLOSE_WAIT:
                        /*		so->so_error = ECONNRESET; */
                close:
                        tp->t_state = TCPS_CLOSED;
                        tcpstat.tcps_drops++;
                        tp = tcp_close(tp);
                        goto drop;

                case TCPS_CLOSING:
                case TCPS_LAST_ACK:
                case TCPS_TIME_WAIT:
                        tp = tcp_close(tp);
                        goto drop;
                }

        /*
         * If a SYN is in the window, then this is an
         * error and we send an RST and drop the connection.
         */
        if (tiflags & TH_SYN) {
                tp = tcp_drop(tp, 0);
                goto dropwithreset;
        }

        /*
         * If the ACK bit is off we drop the segment and return.
         */
        if ((tiflags & TH_ACK) == 0)
                goto drop;

        /*
         * Ack processing.
         */
        switch (tp->t_state) {
                /*
                 * In SYN_RECEIVED state if the ack ACKs our SYN then enter
                 * ESTABLISHED state and continue processing, otherwise
                 * send an RST.  una<=ack<=max
                 */
        case TCPS_SYN_RECEIVED:

                if (SEQ_GT(tp->snd_una, ti->ti_ack) || SEQ_GT(ti->ti_ack, tp->snd_max))
                        goto dropwithreset;
                tcpstat.tcps_connects++;
                tp->t_state = TCPS_ESTABLISHED;
                /*
                 * The sent SYN is ack'ed with our sequence number +1
                 * The first data byte already in the buffer will get
                 * lost if no correction is made.  This is only needed for
                 * SS_CTL since the buffer is empty otherwise.
                 * tp->snd_una++; or:
                 */
                tp->snd_una = ti->ti_ack;
                if (so->so_state & SS_CTL) {
                        /* So tcp_ctl reports the right state */
                        ret = tcp_ctl(so);
                        if (ret == 1) {
                                soisfconnected(so);
                                so->so_state &= ~SS_CTL; /* success XXX */
                        } else if (ret == 2) {
                                so->so_state = SS_NOFDREF; /* CTL_CMD */
                        } else {
                                needoutput = 1;
                                tp->t_state = TCPS_FIN_WAIT_1;
                        }
                } else {
                        soisfconnected(so);
                }

                /* Do window scaling? */
                /*		if ((tp->t_flags & (TF_RCVD_SCALE|TF_REQ_SCALE)) ==
                 *			(TF_RCVD_SCALE|TF_REQ_SCALE)) {
                 *			tp->snd_scale = tp->requested_s_scale;
                 *			tp->rcv_scale = tp->request_r_scale;
                 *		}
                 */
                (void)tcp_reass(tp, (struct tcpiphdr *)0, (struct SLIRPmbuf *)0);
                tp->snd_wl1 = ti->ti_seq - 1;
                /* Avoid ack processing; snd_una==ti_ack  =>  dup ack */
                goto synrx_to_est;
                /* fall into ... */

                /*
                 * In ESTABLISHED state: drop duplicate ACKs; ACK out of range
                 * ACKs.  If the ack is in the range
                 *	tp->snd_una < ti->ti_ack <= tp->snd_max
                 * then advance tp->snd_una to ti->ti_ack and drop
                 * data from the retransmission queue.  If this ACK reflects
                 * more up to date window information we update our window information.
                 */
        case TCPS_ESTABLISHED:
        case TCPS_FIN_WAIT_1:
        case TCPS_FIN_WAIT_2:
        case TCPS_CLOSE_WAIT:
        case TCPS_CLOSING:
        case TCPS_LAST_ACK:
        case TCPS_TIME_WAIT:

                if (SEQ_LEQ(ti->ti_ack, tp->snd_una)) {
                        if (ti->ti_len == 0 && tiwin == tp->snd_wnd) {
                                tcpstat.tcps_rcvdupack++;
                                DEBUG_MISC((dfd, " dup ack  m = %lx  so = %lx \n", (long)m, (long)so));
                                /*
                                 * If we have outstanding data (other than
                                 * a window probe), this is a completely
                                 * duplicate ack (ie, window info didn't
                                 * change), the ack is the biggest we've
                                 * seen and we've seen exactly our rexmt
                                 * threshold of them, assume a packet
                                 * has been dropped and retransmit it.
                                 * Kludge snd_nxt & the congestion
                                 * window so we send only this one
                                 * packet.
                                 *
                                 * We know we're losing at the current
                                 * window size so do congestion avoidance
                                 * (set ssthresh to half the current window
                                 * and pull our congestion window back to
                                 * the new ssthresh).
                                 *
                                 * Dup acks mean that packets have left the
                                 * network (they're now cached at the receiver)
                                 * so bump cwnd by the amount in the receiver
                                 * to keep a constant cwnd packets in the
                                 * network.
                                 */
                                if (tp->t_timer[TCPT_REXMT] == 0 || ti->ti_ack != tp->snd_una)
                                        tp->t_dupacks = 0;
                                else if (++tp->t_dupacks == tcprexmtthresh) {
                                        tcp_seq onxt = tp->snd_nxt;
                                        u_int win = min(tp->snd_wnd, tp->snd_cwnd) / 2 / tp->t_maxseg;

                                        if (win < 2)
                                                win = 2;
                                        tp->snd_ssthresh = win * tp->t_maxseg;
                                        tp->t_timer[TCPT_REXMT] = 0;
                                        tp->t_rtt = 0;
                                        tp->snd_nxt = ti->ti_ack;
                                        tp->snd_cwnd = tp->t_maxseg;
                                        (void)tcp_output(tp);
                                        tp->snd_cwnd = tp->snd_ssthresh + tp->t_maxseg * tp->t_dupacks;
                                        if (SEQ_GT(onxt, tp->snd_nxt))
                                                tp->snd_nxt = onxt;
                                        goto drop;
                                } else if (tp->t_dupacks > tcprexmtthresh) {
                                        tp->snd_cwnd += tp->t_maxseg;
                                        (void)tcp_output(tp);
                                        goto drop;
                                }
                        } else
                                tp->t_dupacks = 0;
                        break;
                }
        synrx_to_est:
                /*
                 * If the congestion window was inflated to account
                 * for the other side's cached packets, retract it.
                 */
                if (tp->t_dupacks > tcprexmtthresh && tp->snd_cwnd > tp->snd_ssthresh)
                        tp->snd_cwnd = tp->snd_ssthresh;
                tp->t_dupacks = 0;
                if (SEQ_GT(ti->ti_ack, tp->snd_max)) {
                        tcpstat.tcps_rcvacktoomuch++;
                        goto dropafterack;
                }
                acked = ti->ti_ack - tp->snd_una;
                tcpstat.tcps_rcvackpack++;
                tcpstat.tcps_rcvackbyte += acked;

                /*
                 * If we have a timestamp reply, update smoothed
                 * round trip time.  If no timestamp is present but
                 * transmit timer is running and timed sequence
                 * number was acked, update smoothed round trip time.
                 * Since we now have an rtt measurement, cancel the
                 * timer backoff (cf., Phil Karn's retransmit alg.).
                 * Recompute the initial retransmit timer.
                 */
                /*		if (ts_present)
                 *			tcp_xmit_timer(tp, tcp_now-ts_ecr+1);
                 *		else
                 */
                if (tp->t_rtt && SEQ_GT(ti->ti_ack, tp->t_rtseq))
                        tcp_xmit_timer(tp, tp->t_rtt);

                /*
                 * If all outstanding data is acked, stop retransmit
                 * timer and remember to restart (more output or persist).
                 * If there is more data to be acked, restart retransmit
                 * timer, using current (possibly backed-off) value.
                 */
                if (ti->ti_ack == tp->snd_max) {
                        tp->t_timer[TCPT_REXMT] = 0;
                        needoutput = 1;
                } else if (tp->t_timer[TCPT_PERSIST] == 0)
                        tp->t_timer[TCPT_REXMT] = tp->t_rxtcur;
                /*
                 * When new data is acked, open the congestion window.
                 * If the window gives us less than ssthresh packets
                 * in flight, open exponentially (maxseg per packet).
                 * Otherwise open linearly: maxseg per window
                 * (maxseg^2 / cwnd per packet).
                 */
                {
                        u_int cw = tp->snd_cwnd;
                        u_int incr = tp->t_maxseg;

                        if (cw > tp->snd_ssthresh)
                                incr = incr * incr / cw;
                        tp->snd_cwnd = min(cw + incr, TCP_MAXWIN << tp->snd_scale);
                }
                if (acked > so->so_snd.sb_cc) {
                        tp->snd_wnd -= so->so_snd.sb_cc;
                        sbdrop(&so->so_snd, (int)so->so_snd.sb_cc);
                        ourfinisacked = 1;
                } else {
                        sbdrop(&so->so_snd, acked);
                        tp->snd_wnd -= acked;
                        ourfinisacked = 0;
                }
                /*
                 * XXX sowwakup is called when data is acked and there's room for
                 * for more data... it should read() the socket
                 */
                /*		if (so->so_snd.sb_flags & SB_NOTIFY)
                 *			sowwakeup(so);
                 */
                tp->snd_una = ti->ti_ack;
                if (SEQ_LT(tp->snd_nxt, tp->snd_una))
                        tp->snd_nxt = tp->snd_una;

                switch (tp->t_state) {

                        /*
                         * In FIN_WAIT_1 STATE in addition to the processing
                         * for the ESTABLISHED state if our FIN is now acknowledged
                         * then enter FIN_WAIT_2.
                         */
                case TCPS_FIN_WAIT_1:
                        if (ourfinisacked) {
                                /*
                                 * If we can't receive any more
                                 * data, then closing user can proceed.
                                 * Starting the timer is contrary to the
                                 * specification, but if we don't get a FIN
                                 * we'll hang forever.
                                 */
                                if (so->so_state & SS_FCANTRCVMORE) {
                                        soisfdisconnected(so);
                                        tp->t_timer[TCPT_2MSL] = tcp_maxidle;
                                }
                                tp->t_state = TCPS_FIN_WAIT_2;
                        }
                        break;

                        /*
                         * In CLOSING STATE in addition to the processing for
                         * the ESTABLISHED state if the ACK acknowledges our FIN
                         * then enter the TIME-WAIT state, otherwise ignore
                         * the segment.
                         */
                case TCPS_CLOSING:
                        if (ourfinisacked) {
                                tp->t_state = TCPS_TIME_WAIT;
                                tcp_canceltimers(tp);
                                tp->t_timer[TCPT_2MSL] = 2 * TCPTV_MSL;
                                soisfdisconnected(so);
                        }
                        break;

                        /*
                         * In LAST_ACK, we may still be waiting for data to drain
                         * and/or to be acked, as well as for the ack of our FIN.
                         * If our FIN is now acknowledged, delete the TCB,
                         * enter the closed state and return.
                         */
                case TCPS_LAST_ACK:
                        if (ourfinisacked) {
                                tp = tcp_close(tp);
                                goto drop;
                        }
                        break;

                        /*
                         * In TIME_WAIT state the only thing that should arrive
                         * is a retransmission of the remote FIN.  Acknowledge
                         * it and restart the finack timer.
                         */
                case TCPS_TIME_WAIT:
                        tp->t_timer[TCPT_2MSL] = 2 * TCPTV_MSL;
                        goto dropafterack;
                }
        } /* switch(tp->t_state) */

step6:
        /*
         * Update window information.
         * Don't look at window if no ACK: TAC's send garbage on first SYN.
         */
        if ((tiflags & TH_ACK) && (SEQ_LT(tp->snd_wl1, ti->ti_seq) ||
                                   (tp->snd_wl1 == ti->ti_seq &&
                                    (SEQ_LT(tp->snd_wl2, ti->ti_ack) || (tp->snd_wl2 == ti->ti_ack && tiwin > tp->snd_wnd))))) {
                /* keep track of pure window updates */
                if (ti->ti_len == 0 && tp->snd_wl2 == ti->ti_ack && tiwin > tp->snd_wnd)
                        tcpstat.tcps_rcvwinupd++;
                tp->snd_wnd = tiwin;
                tp->snd_wl1 = ti->ti_seq;
                tp->snd_wl2 = ti->ti_ack;
                if (tp->snd_wnd > tp->max_sndwnd)
                        tp->max_sndwnd = tp->snd_wnd;
                needoutput = 1;
        }

        /*
         * Process segments with URG.
         */
        if ((tiflags & TH_URG) && ti->ti_urp && TCPS_HAVERCVDFIN(tp->t_state) == 0) {
                /*
                 * This is a kludge, but if we receive and accept
                 * random urgent pointers, we'll crash in
                 * soreceive.  It's hard to imagine someone
                 * actually wanting to send this much urgent data.
                 */
                if (ti->ti_urp + so->so_rcv.sb_cc > so->so_rcv.sb_datalen) {
                        ti->ti_urp = 0;
                        tiflags &= ~TH_URG;
                        goto dodata;
                }
                /*
                 * If this segment advances the known urgent pointer,
                 * then mark the data stream.  This should not happen
                 * in CLOSE_WAIT, CLOSING, LAST_ACK or TIME_WAIT STATES since
                 * a FIN has been received from the remote side.
                 * In these states we ignore the URG.
                 *
                 * According to RFC961 (Assigned Protocols),
                 * the urgent pointer points to the last octet
                 * of urgent data.  We continue, however,
                 * to consider it to indicate the first octet
                 * of data past the urgent section as the original
                 * spec states (in one of two places).
                 */
                if (SEQ_GT(ti->ti_seq + ti->ti_urp, tp->rcv_up)) {
                        tp->rcv_up = ti->ti_seq + ti->ti_urp;
                        so->so_urgc = so->so_rcv.sb_cc + (tp->rcv_up - tp->rcv_nxt); /* -1; */
                        tp->rcv_up = ti->ti_seq + ti->ti_urp;
                }
        } else
                /*
                 * If no out of band data is expected,
                 * pull receive urgent pointer along
                 * with the receive window.
                 */
                if (SEQ_GT(tp->rcv_nxt, tp->rcv_up))
                tp->rcv_up = tp->rcv_nxt;
dodata:

        /*
         * Process the segment text, merging it into the TCP sequencing queue,
         * and arranging for acknowledgment of receipt if necessary.
         * This process logically involves adjusting tp->rcv_wnd as data
         * is presented to the user (this happens in tcp_usrreq.c,
         * case PRU_RCVD).  If a FIN has already been received on this
         * connection then we just ignore the text.
         */
        if ((ti->ti_len || (tiflags & TH_FIN)) && TCPS_HAVERCVDFIN(tp->t_state) == 0) {
                TCP_REASS(tp, ti, m, so, tiflags);
                /*
                 * Note the amount of data that peer has sent into
                 * our window, in order to estimate the sender's
                 * buffer size.
                 */
                len = so->so_rcv.sb_datalen - (tp->rcv_adv - tp->rcv_nxt);
        } else {
                m_free(m);
                tiflags &= ~TH_FIN;
        }

        /*
         * If FIN is received ACK the FIN and let the user know
         * that the connection is closing.
         */
        if (tiflags & TH_FIN) {
                if (TCPS_HAVERCVDFIN(tp->t_state) == 0) {
                        /*
                         * If we receive a FIN we can't send more data,
                         * set it SS_FDRAIN
                         * Shutdown the socket if there is no rx data in the
                         * buffer.
                         * soread() is called on completion of shutdown() and
                         * will got to TCPS_LAST_ACK, and use tcp_output()
                         * to send the FIN.
                         */
                        /*			sofcantrcvmore(so); */
                        sofwdrain(so);

                        tp->t_flags |= TF_ACKNOW;
                        tp->rcv_nxt++;
                }
                switch (tp->t_state) {

                        /*
                         * In SYN_RECEIVED and ESTABLISHED STATES
                         * enter the CLOSE_WAIT state.
                         */
                case TCPS_SYN_RECEIVED:
                case TCPS_ESTABLISHED:
                        if (so->so_emu == EMU_CTL) /* no shutdown on socket */
                                tp->t_state = TCPS_LAST_ACK;
                        else
                                tp->t_state = TCPS_CLOSE_WAIT;
                        break;

                        /*
                         * If still in FIN_WAIT_1 STATE FIN has not been acked so
                         * enter the CLOSING state.
                         */
                case TCPS_FIN_WAIT_1:
                        tp->t_state = TCPS_CLOSING;
                        break;

                        /*
                         * In FIN_WAIT_2 state enter the TIME_WAIT state,
                         * starting the time-wait timer, turning off the other
                         * standard timers.
                         */
                case TCPS_FIN_WAIT_2:
                        tp->t_state = TCPS_TIME_WAIT;
                        tcp_canceltimers(tp);
                        tp->t_timer[TCPT_2MSL] = 2 * TCPTV_MSL;
                        soisfdisconnected(so);
                        break;

                        /*
                         * In TIME_WAIT state restart the 2 MSL time_wait timer.
                         */
                case TCPS_TIME_WAIT:
                        tp->t_timer[TCPT_2MSL] = 2 * TCPTV_MSL;
                        break;
                }
        }

        /*
         * If this is a small packet, then ACK now - with Nagel
         *      congestion avoidance sender won't send more until
         *      he gets an ACK.
         *
         * See above.
         */
        /*	if (ti->ti_len && (unsigned)ti->ti_len < tp->t_maxseg) {
         */
        /*	if ((ti->ti_len && (unsigned)ti->ti_len < tp->t_maxseg &&
         *		(so->so_iptos & IPTOS_LOWDELAY) == 0) ||
         *	       ((so->so_iptos & IPTOS_LOWDELAY) &&
         *	       ((struct tcpiphdr_2 *)ti)->first_char == (char)27)) {
         */
        if (ti->ti_len && (unsigned)ti->ti_len <= 5 && ((struct tcpiphdr_2 *)ti)->first_char == (char)27) {
                tp->t_flags |= TF_ACKNOW;
        }

        /*
         * Return any desired output.
         */
        if (needoutput || (tp->t_flags & TF_ACKNOW)) {
                (void)tcp_output(tp);
        }
        return;

dropafterack:
        /*
         * Generate an ACK dropping incoming segment if it occupies
         * sequence space, where the ACK reflects our state.
         */
        if (tiflags & TH_RST)
                goto drop;
        m_freem(m);
        tp->t_flags |= TF_ACKNOW;
        (void)tcp_output(tp);
        return;

dropwithreset:
        /* reuses m if m!=NULL, m_free() unnecessary */
        if (tiflags & TH_ACK)
                tcp_respond(tp, ti, m, (tcp_seq)0, ti->ti_ack, TH_RST);
        else {
                if (tiflags & TH_SYN)
                        ti->ti_len++;
                tcp_respond(tp, ti, m, ti->ti_seq + ti->ti_len, (tcp_seq)0, TH_RST | TH_ACK);
        }

        return;

drop:
        /*
         * Drop space held by incoming segment and return.
         */
        m_free(m);

        return;
}

/* , ts_present, ts_val, ts_ecr) */
/*	int *ts_present;
 *	u_int32_t *ts_val, *ts_ecr;
 */
void tcp_dooptions(tp, cp, cnt, ti) struct tcpcb *tp;
u_char *cp;
int cnt;
struct tcpiphdr *ti;
{
        u_int16_t mss;
        int opt, optlen;

        DEBUG_CALL("tcp_dooptions");
        DEBUG_ARGS((dfd, " tp = %lx  cnt=%i \n", (long)tp, cnt));

        for (; cnt > 0; cnt -= optlen, cp += optlen) {
                opt = cp[0];
                if (opt == TCPOPT_EOL)
                        break;
                if (opt == TCPOPT_NOP)
                        optlen = 1;
                else {
                        optlen = cp[1];
                        if (optlen <= 0)
                                break;
                }
                switch (opt) {

                default:
                        continue;

                case TCPOPT_MAXSEG:
                        if (optlen != TCPOLEN_MAXSEG)
                                continue;
                        if (!(ti->ti_flags & TH_SYN))
                                continue;
                        memcpy((char *)&mss, (char *)cp + 2, sizeof(mss));
                        NTOHS(mss);
                        (void)tcp_mss(tp, mss); /* sets t_maxseg */
                        break;

                        /*		case TCPOPT_WINDOW:
                         *			if (optlen != TCPOLEN_WINDOW)
                         *				continue;
                         *			if (!(ti->ti_flags & TH_SYN))
                         *				continue;
                         *			tp->t_flags |= TF_RCVD_SCALE;
                         *			tp->requested_s_scale = min(cp[2], TCP_MAX_WINSHIFT);
                         *			break;
                         */
                        /*		case TCPOPT_TIMESTAMP:
                         *			if (optlen != TCPOLEN_TIMESTAMP)
                         *				continue;
                         *			*ts_present = 1;
                         *			memcpy((char *) ts_val, (char *)cp + 2, sizeof(*ts_val));
                         *			NTOHL(*ts_val);
                         *			memcpy((char *) ts_ecr, (char *)cp + 6, sizeof(*ts_ecr));
                         *			NTOHL(*ts_ecr);
                         *
                         */                        /*
 *			 * A timestamp received in a SYN makes
 *			 * it ok to send timestamp requests and replies.
 *			 */
                        /*			if (ti->ti_flags & TH_SYN) {
                         *				tp->t_flags |= TF_RCVD_TSTMP;
                         *				tp->ts_recent = *ts_val;
                         *				tp->ts_recent_age = tcp_now;
                         *			}
                         */
                        break;
                }
        }
}

/*
 * Pull out of band byte out of a segment so
 * it doesn't appear in the user's data queue.
 * It is still reflected in the segment length for
 * sequencing purposes.
 */

#ifdef notdef

void tcp_pulloutofband(so, ti, m) struct SLIRPsocket *so;
struct tcpiphdr *ti;
struct SLIRPmbuf *m;
{
        int cnt = ti->ti_urp - 1;

        while (cnt >= 0) {
                if (m->m_len > cnt) {
                        char *cp = mtod(m, SLIRPcaddr_t) + cnt;
                        struct tcpcb *tp = sototcpcb(so);

                        tp->t_iobc = *cp;
                        tp->t_oobflags |= TCPOOB_HAVEDATA;
                        memcpy(sp, cp + 1, (unsigned)(m->m_len - cnt - 1));
                        m->m_len--;
                        return;
                }
                cnt -= m->m_len;
                m = m->m_next; /* XXX WRONG! Fix it! */
                if (m == 0)
                        break;
        }
        panic("tcp_pulloutofband");
}

#endif /* notdef */

/*
 * Collect new round-trip time estimate
 * and update averages and current timeout.
 */

void tcp_xmit_timer(tp, rtt) struct tcpcb *tp;
int rtt;
{
        short delta;

        DEBUG_CALL("tcp_xmit_timer");
        DEBUG_ARG("tp = %lx", (long)tp);
        DEBUG_ARG("rtt = %d", rtt);

        tcpstat.tcps_rttupdated++;
        if (tp->t_srtt != 0) {
                /*
                 * srtt is stored as fixed point with 3 bits after the
                 * binary point (i.e., scaled by 8).  The following magic
                 * is equivalent to the smoothing algorithm in rfc793 with
                 * an alpha of .875 (srtt = rtt/8 + srtt*7/8 in fixed
                 * point).  Adjust rtt to origin 0.
                 */
                delta = rtt - 1 - (tp->t_srtt >> TCP_RTT_SHIFT);
                if ((tp->t_srtt += delta) <= 0)
                        tp->t_srtt = 1;
                /*
                 * We accumulate a smoothed rtt variance (actually, a
                 * smoothed mean difference), then set the retransmit
                 * timer to smoothed rtt + 4 times the smoothed variance.
                 * rttvar is stored as fixed point with 2 bits after the
                 * binary point (scaled by 4).  The following is
                 * equivalent to rfc793 smoothing with an alpha of .75
                 * (rttvar = rttvar*3/4 + |delta| / 4).  This replaces
                 * rfc793's wired-in beta.
                 */
                if (delta < 0)
                        delta = -delta;
                delta -= (tp->t_rttvar >> TCP_RTTVAR_SHIFT);
                if ((tp->t_rttvar += delta) <= 0)
                        tp->t_rttvar = 1;
        } else {
                /*
                 * No rtt measurement yet - use the unsmoothed rtt.
                 * Set the variance to half the rtt (so our first
                 * retransmit happens at 3*rtt).
                 */
                tp->t_srtt = rtt << TCP_RTT_SHIFT;
                tp->t_rttvar = rtt << (TCP_RTTVAR_SHIFT - 1);
        }
        tp->t_rtt = 0;
        tp->t_rxtshift = 0;

        /*
         * the retransmit should happen at rtt + 4 * rttvar.
         * Because of the way we do the smoothing, srtt and rttvar
         * will each average +1/2 tick of bias.  When we compute
         * the retransmit timer, we want 1/2 tick of rounding and
         * 1 extra tick because of +-1/2 tick uncertainty in the
         * firing of the timer.  The bias will give us exactly the
         * 1.5 tick we need.  But, because the bias is
         * statistical, we have to test that we don't drop below
         * the minimum feasible timer (which is 2 ticks).
         */
        TCPT_RANGESET(tp->t_rxtcur, TCP_REXMTVAL(tp), (short)tp->t_rttmin, TCPTV_REXMTMAX); /* XXX */

        /*
         * We received an ack for a packet that wasn't retransmitted;
         * it is probably safe to discard any error indications we've
         * received recently.  This isn't quite right, but close enough
         * for now (a route might have failed after we sent a segment,
         * and the return path might not be symmetrical).
         */
        tp->t_softerror = 0;
}

/*
 * Determine a reasonable value for maxseg size.
 * If the route is known, check route for mtu.
 * If none, use an mss that can be handled on the outgoing
 * interface without forcing IP to fragment; if bigger than
 * an SLIRPmbuf cluster (MCLBYTES), round down to nearest multiple of MCLBYTES
 * to utilize large SLIRPmbufs.  If no route is found, route has no mtu,
 * or the destination isn't local, use a default, hopefully conservative
 * size (usually 512 or the default IP max size, but no more than the mtu
 * of the interface), as we can't discover anything about intervening
 * gateways or networks.  We also initialize the congestion/slow start
 * window to be a single segment if the destination isn't local.
 * While looking at the routing entry, we also initialize other path-dependent
 * parameters from pre-set or cached values in the routing entry.
 */

int tcp_mss(tp, offer) struct tcpcb *tp;
u_int offer;
{
        struct SLIRPsocket *so = tp->t_socket;
        int mss;

        DEBUG_CALL("tcp_mss");
        DEBUG_ARG("tp = %lx", (long)tp);
        DEBUG_ARG("offer = %d", offer);

        mss = min(if_mtu, if_mru) - sizeof(struct tcpiphdr);
        if (offer)
                mss = min(mss, offer);
        mss = max(mss, 32);
        if (mss < tp->t_maxseg || offer != 0)
                tp->t_maxseg = mss;

        tp->snd_cwnd = mss;

        sbreserve(&so->so_snd, tcp_sndspace + ((tcp_sndspace % mss) ? (mss - (tcp_sndspace % mss)) : 0));
        sbreserve(&so->so_rcv, tcp_rcvspace + ((tcp_rcvspace % mss) ? (mss - (tcp_rcvspace % mss)) : 0));

        DEBUG_MISC((dfd, " returning mss = %d\n", mss));

        return mss;
}
